* module/language/tree-il/cse.scm (cse): When trying to fold
conditionals, only look at entries in the database that were added in
test context.
* test-suite/tests/cse.test ("cse"): Add a test case.
* test-suite/tests/cse.test (pass-if-cse): Fix-letrec and canonicalize
the output, so that unreferenced failure continuations get trimmed.
("cse"): Fix the two tests regarding bailout info.
* module/language/tree-il/cse.scm: New pass, some simple common
subexpression elimination with effects analysis.
* test-suite/tests/cse.test: New test.
* test-suite/Makefile.am:
* module/Makefile.am: Adapt.
